Development of informatization allows people to communicate at any moment and everywhere and widespread use of various communication equipments and technologies greatly facilitates life and enhances work efficiency. However, social development results in a severe issue, noise. In a noisy environment, definition and intelligibility of communication voice are severely compromised and when noise is high to a certain degree, communication can not proceed, and people's audition and physical and mental health will be injured.
In view of communication under very noisy background, existing art implements noise reduction through the following schemes: on the one hand, acoustics signal processing technology is applied at the sending end of communication earphone to enhance Signal-to-Noise Ratio (SNR) of voice signal picked up by a microphone, allowing remote user to hear speech by the user of the communication earphone clearly. On the other hand, it is necessary to enhance SNR of voice at the receiving end of the communication earphone, allowing local earphone wearer to hear voice signal sent from the remote user clearly.
At present, common speech enhancing methods for sending end of a communication earphone are mainly to utilize a single or multiple common microphone to pick up signals and then realize speech enhancement with acoustics signal processing method.
Speech enhancement with a single microphone is generally referred to as single channel spectral subtraction speech enhancement technology (see China patent of invention publications CN1684143A and CN101477800A). This technology generally estimates energy of stationary noise in current voice by analyzing historical data and then achieve speech enhancement by canceling noise in voice with spectral subtraction method. However, this method can only suppress steady noise such as white noise and has limited noise reduction amount. Too big noise reduction amount may impair voice and for nonsteady noise such as surrounding voice noise and knocking noise, it is impossible to estimate its energy accurately, and hence impossible to cancel it effectively.
Another method that can effectively suppress nonsteady noise is to apply the speech enhancement technology with microphone array consisting of two or more microphones (see China patent of invention publications CN101466055A and CN1967158A). With this technology, generally, a signal received by one microphone is used as reference signal, and noise component in signal picked up by another microphone is estimated and canceled out in real time with an adaptive filtering method, while leaving speech component, hence achieving speech enhancement purpose. The multi-microphone technology may suppress nonsteady noise and has noise reduction amount greater than that of single microphone technology. However, this method requires accurate detection of speech state, otherwise the speech may be canceled as noise.
Some prior multi-microphone technologies use directive microphones (see China patent of invention publication CN101466055A) or a plurality of microphones to form directivity (see China patent of invention publication CN101466056A) to detect voice from a specific direction, which is only applicable to the case of fixed microphone array shape and fixed location and direction with respect to user. When the user deviate from the directing scope of the microphone array or the shape or position of microphone array changes resulting microphone array direction deviating the user, the speech may be suppressed as noise. The case is for example as shown in FIG. 1, in which the microphone is mounted on earphone flexible cord.
In the communication earphone shown in FIG. 1, the microphone 112 is mounted on the earphone flexible cord. In specific application process, this earphone microphone is not fixed relative to the user's mouth and it forms a microphone array with non-fixed shape together with microphones mounted on other positions of the earphone. In communication, the user would place the microphone on flexible cord at any location near the mouth. When the user places the microphone outside the directivity scope of the microphone array, speech may be treated as noise and then it is impossible to detect speech accurately with the directivity of microphone array.
Speech enhancing methods commonly used presently at receiving end of communication earphone mainly adopt two technologies. One is to adopt an automatic volume control technology (see China patent of invention publication CN1507293A), i.e, automatically enhancing power supplied to the speaker unit when outside noise is high, which is a passive method limited by the industry standard for power of speaker unit itself and the sound pressure fed into ears by an inserted earplug. It is not possible to enhance volume of speaker unit unlimitedly, and the high intensity speech emitted by the speaker may damage the user's audition and physical and mental health. Another method is to apply a noise control technology that combines traditional active/passive technologies to a communication earphone (see China patent of invention publication CN101432798A). The earphone may be classified into head worn and earplug. The earplug type earphone typically takes a sealed coupling form between leather sheathes and ears. On the one hand, sound absorption and sound isolation of materials is used to depress intermediate and high frequency noise. On the other hand, low frequency (mainly below 300 Hz) noise is effectively depressed with active noise control technologies, thus realizing good control over outside noise in the full band and enhancing SNR of speech at the receiving end of communication earphone effectively.